Position sensors are used to provide inputs for a variety of electronic devices. Some of these sensors are electromechanical devices, such as the ubiquitous “mouse” that is used to provide position input signals to digital computers. Other sensors, which are non-mechanical, usually make use of electrostatic or magnetic fields to provide position information. An example of an electrostatic sensor is a capacitive button switch, which is actuated when the user places a finger thereon; in so doing the user effectively increases the capacitance of a capacitor, with the resulting increase in capacitive current being sensed to indicate actuation of the button.
Non-mechanical sensors are advantageous in that they have no moving parts and moreover are, in theory at least, not restricted to operation over a small area such as a mousepad or the like. Actually, however, because of configuration and sensitivity considerations, these sensors are limited to a small area; indeed, when they are used as “pushbuttons,” this is a desirable attribute of capacitive sensors.
Electromechanical sensors are limited by their construction to detection of specific types of user movements. For example, a mouse can detect position along a two-dimensional surface and transmit the user's actuation of “click” buttons mounted on the mouse; three-dimensional location and gestures other than the familiar button click, however, are beyond the mouse's capacity to detect. The prior electrostatic and magnetic sensors suffer from the same disabilities.
In fact, determining the position, mass distribution or orientation of an object within a defined space represents a highly complex problem. Solutions have been proposed for free space measurements; see, e.g., U.S. Pat. Nos. 5,844,415 and 6,066,954. However, these solutions require electrodes arranged throughout the space of interest. This may not be practical in all applications. For example, it may be inconvenient to distribute electrodes in spaces the size of a room, or the necessary locations may be physically inaccessible or render the electrodes susceptible to damage.